This invention pertains to semiconductor processing methods in which materials are exposed to liquid solutions comprising fluorine-containing species.
Many semiconductor fabrication processes comprise one or more steps wherein a material is exposed to fluorine-containing species. The fluorine-containing species can be, for example, in the form of hydrogen fluoride. An example use of hydrogen fluoride in semiconductor fabrication processes is to strip silicon dioxide from a surface. Another example use of hydrogen fluoride is to passivate a silicon surface (i.e., to react hydrogen with dangling silicon bonds).
Passivation of silicon surfaces and/or stripping of silicon dioxide can be utilized to enhance formation of hemispherical grain (HSG) polysilicon. Example HSG polysilicon fabrication processes are described in U.S. Pat. Nos. 5,634,974 and 5,691,228, which are incorporated herein by reference. Generally, the fabrication processes disclosed in such patents comprise forming a layer of amorphous silicon, passivating and/or cleaning the layer of amorphous silicon with hydrofluoric acid, and converting the amorphous silicon to HSG polysilicon. A method of converting amorphous silicon to HSG polysilicon comprises seeding the amorphous silicon by, for example, irradiation or doping, to form nucleation centers for subsequent growth of individual grains of HSG polysilicon. HSG polysilicon is grown from the nucleation centers by annealing the seeded amorphous silicon at, for example, a temperature of from about 200xc2x0 C. to about 1500xc2x0 C. and a pressure of from about 1xc3x9710xe2x88x928 Torr to about 1 atmosphere for a time of from about one second to about five hours.
The hydrofluoric acid treatments utilized in the above-described fabrication of HSG polysilicon either comprise an HF vapor clean, or a dip within an HF solution. If a dip is utilized, the temperature of the dip solution will be about 21.5xc2x0 C. The dip solution is generally kept within a vessel configured to cool the dip solution to maintain a temperature of about 21.5xc2x0 C. An advantage of the 21.5xc2x0 C. temperature is that it is a temperature which has traditionally been used for HF dipping, and accordingly there is a large amount of information available pertaining to appropriate dipping times and conditions for various applications. Another advantage is that the equipment presently manufactured for dipping within HF solutions is configured to maintain a temperature of about 21.5xc2x0 C. If the temperature were to vary significantly, it would introduce unwanted variability into a fabrication process.
It is desired to develop alternative methods of utilizing fluorine-containing species for treating materials during semiconductive fabrication processes.
In one aspect, the invention encompasses a semiconductor processing method wherein a surface is contacted with a liquid solution comprising one or more fluorine-containing species and a temperature of at least about 40xc2x0 C.
In another aspect, the invention encompasses a method of passivating a silicon-comprising layer wherein the layer is contacted with a liquid solution comprising hydrogen fluoride and a temperature of at least about 40xc2x0 C.
In another aspect, the invention encompasses a method of forming HSG polysilicon. A layer comprising substantially amorphous silicon is formed over a substrate. The layer comprising substantially amorphous silicon is contacted with a liquid solution comprising one or more fluorine-containing species and a temperature of at least about 40xc2x0 C. The layer comprising substantially amorphous silicon is seeded and annealed to convert at least a portion of the layer to HSG polysilicon.
In yet another aspect, the invention encompasses a method of forming a wordline. A silicon layer is formed over a substrate. The silicon layer is passivated by contacting it with a liquid solution comprising hydrogen fluoride. The liquid solution is at a temperature of at least about 40xc2x0 C. during the contacting. After the passivating, a silicide layer is formed over the silicon layer.